mm: compaction: introduce isolate_freepages_range()

This commit introduces isolate_freepages_range() function which
generalises isolate_freepages_block() so that it can be used on
arbitrary PFN ranges.

isolate_freepages_block() is left with only minor changes.

Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Tested-by: Rob Clark <rob.clark@linaro.org>
Tested-by: Ohad Ben-Cohen <ohad@wizery.com>
Tested-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Tested-by: Robert Nelson <robertcnelson@gmail.com>
Tested-by: Barry Song <Baohua.Song@csr.com>

diff --git a/mm/compaction.c b/mm/compaction.c
index d9d7b35d39330ab3644e0f40ae17cbd4a79b5793..06b198fa9abe2e0f1452e8c996c549036afdb258 100644 (file)
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -54,24 +54,20 @@ static unsigned long release_freepages(struct list_head *freelist)
        return count;
 }
 
-/* Isolate free pages onto a private freelist. Must hold zone->lock */
-static unsigned long isolate_freepages_block(struct zone *zone,
-                               unsigned long blockpfn,
-                               struct list_head *freelist)
+/*
+ * Isolate free pages onto a private freelist. Caller must hold zone->lock.
+ * If @strict is true, will abort returning 0 on any invalid PFNs or non-free
+ * pages inside of the pageblock (even though it may still end up isolating
+ * some pages).
+ */
+static unsigned long isolate_freepages_block(unsigned long blockpfn,
+                               unsigned long end_pfn,
+                               struct list_head *freelist,
+                               bool strict)
 {
-       unsigned long zone_end_pfn, end_pfn;
        int nr_scanned = 0, total_isolated = 0;
        struct page *cursor;
 
-       /* Get the last PFN we should scan for free pages at */
-       zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
-       end_pfn = min(blockpfn + pageblock_nr_pages, zone_end_pfn);
-
-       /* Find the first usable PFN in the block to initialse page cursor */
-       for (; blockpfn < end_pfn; blockpfn++) {
-               if (pfn_valid_within(blockpfn))
-                       break;
-       }
        cursor = pfn_to_page(blockpfn);
 
        /* Isolate free pages. This assumes the block is valid */
@@ -79,15 +75,23 @@ static unsigned long isolate_freepages_block(struct zone *zone,
                int isolated, i;
                struct page *page = cursor;
 
-               if (!pfn_valid_within(blockpfn))
+               if (!pfn_valid_within(blockpfn)) {
+                       if (strict)
+                               return 0;
                        continue;
+               }
                nr_scanned++;
 
-               if (!PageBuddy(page))
+               if (!PageBuddy(page)) {
+                       if (strict)
+                               return 0;
                        continue;
+               }
 
                /* Found a free page, break it into order-0 pages */
                isolated = split_free_page(page);
+               if (!isolated && strict)
+                       return 0;
                total_isolated += isolated;
                for (i = 0; i < isolated; i++) {
                        list_add(&page->lru, freelist);
@@ -105,6 +109,73 @@ static unsigned long isolate_freepages_block(struct zone *zone,
        return total_isolated;
 }
 
+/**
+ * isolate_freepages_range() - isolate free pages.
+ * @start_pfn: The first PFN to start isolating.
+ * @end_pfn:   The one-past-last PFN.
+ *
+ * Non-free pages, invalid PFNs, or zone boundaries within the
+ * [start_pfn, end_pfn) range are considered errors, cause function to
+ * undo its actions and return zero.
+ *
+ * Otherwise, function returns one-past-the-last PFN of isolated page
+ * (which may be greater then end_pfn if end fell in a middle of
+ * a free page).
+ */
+static unsigned long
+isolate_freepages_range(unsigned long start_pfn, unsigned long end_pfn)
+{
+       unsigned long isolated, pfn, block_end_pfn, flags;
+       struct zone *zone = NULL;
+       LIST_HEAD(freelist);
+
+       if (pfn_valid(start_pfn))
+               zone = page_zone(pfn_to_page(start_pfn));
+
+       for (pfn = start_pfn; pfn < end_pfn; pfn += isolated) {
+               if (!pfn_valid(pfn) || zone != page_zone(pfn_to_page(pfn)))
+                       break;
+
+               /*
+                * On subsequent iterations ALIGN() is actually not needed,
+                * but we keep it that we not to complicate the code.
+                */
+               block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
+               block_end_pfn = min(block_end_pfn, end_pfn);
+
+               spin_lock_irqsave(&zone->lock, flags);
+               isolated = isolate_freepages_block(pfn, block_end_pfn,
+                                                  &freelist, true);
+               spin_unlock_irqrestore(&zone->lock, flags);
+
+               /*
+                * In strict mode, isolate_freepages_block() returns 0 if
+                * there are any holes in the block (ie. invalid PFNs or
+                * non-free pages).
+                */
+               if (!isolated)
+                       break;
+
+               /*
+                * If we managed to isolate pages, it is always (1 << n) *
+                * pageblock_nr_pages for some non-negative n.  (Max order
+                * page may span two pageblocks).
+                */
+       }
+
+       /* split_free_page does not map the pages */
+       map_pages(&freelist);
+
+       if (pfn < end_pfn) {
+               /* Loop terminated early, cleanup. */
+               release_freepages(&freelist);
+               return 0;
+       }
+
+       /* We don't use freelists for anything. */
+       return pfn;
+}
+
 /* Returns true if the page is within a block suitable for migration to */
 static bool suitable_migration_target(struct page *page)
 {
@@ -145,7 +216,7 @@ static void isolate_freepages(struct zone *zone,
                                struct compact_control *cc)
 {
        struct page *page;
-       unsigned long high_pfn, low_pfn, pfn;
+       unsigned long high_pfn, low_pfn, pfn, zone_end_pfn, end_pfn;
        unsigned long flags;
        int nr_freepages = cc->nr_freepages;
        struct list_head *freelist = &cc->freepages;
@@ -165,6 +236,8 @@ static void isolate_freepages(struct zone *zone,
         */
        high_pfn = min(low_pfn, pfn);
 
+       zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
+
        /*
         * Isolate free pages until enough are available to migrate the
         * pages on cc->migratepages. We stop searching if the migrate
@@ -201,7 +274,9 @@ static void isolate_freepages(struct zone *zone,
                isolated = 0;
                spin_lock_irqsave(&zone->lock, flags);
                if (suitable_migration_target(page)) {
-                       isolated = isolate_freepages_block(zone, pfn, freelist);
+                       end_pfn = min(pfn + pageblock_nr_pages, zone_end_pfn);
+                       isolated = isolate_freepages_block(pfn, end_pfn,
+                                                          freelist, false);
                        nr_freepages += isolated;
                }
                spin_unlock_irqrestore(&zone->lock, flags);